PREPARATION OF POLYOLEFIN BASED THERMOPLASTIC ELASTOMERS

Abstract: A thermoplastic elastomer consisting of a polyolefin - polyacrylate blend and which is achieved by absorbing an acrylate monomer, initiator and eventually a diacrylate into polyolefin particles after which the temperature is raised and the acrylate polymerises into the polyolefin particles and forms a dispersed phase.

Description: Preparation of polyolefin based thermoplastic elastomers The invention concerns a polyolefine based thermoplastic elastomer which can be prepared without a separate vulcanisation stage and which has polyacrylate as a dispersed phase and which has been achieved by polymerisation of acrylate into the polyolefine matrix. Thermoplastic elastomers are polymers which have the good processing properties of thermoplastics but have the same physical properties as vulcanised rubbers. This com¬ bination of properties can be obtained so that the material has both soft and elastic segments, with low glass transition temperature, t,, and a rigid eventually crystalline segment with a high glass transition temperature or a high melting point. The rigid and soft segments must be thermodynamically incompatible with each other, so that they form separate phases. Thermoplastic elastomers do not need any separate vulcanising stage, in the contrary to conventional rubber, and they can be processed to different articles with the processing methods normally used with thermoplastics, like extrusion, injection moulding and blow moulding. On the contrary to rubber, thermoplastic elastomers can also be reprocessed if necessary, for example when recycling material from the processing stage. Thermoplastic elastomers can be divided into two main groups, block copolymers and thermoplastic/elastomer blends. A well-known example of block copolymers which are thermoplastic elastomers is the anionically polymerised block copolymer of styrene and butadiene (SBS) and the hydrogenised form of the same (SEBS). At room temperature, in these polymers the soft and elastic phase is the continuous phase whereas the rigid phase, polypropylene, is dispersed. The rigid polystyrene gives the material its strength. During the processing the temperature is raised over the glass transition temperature of polysty¬ rene when it melts and the material can flow. Because of the double bonds of butadiene in SBS this thermoplastic elastomer has poor weather resistance. Both in SBS and SEBS polybutadiene and its hydrogenated form is the continues phase, from which follows that the both have low oil resistance. An other drawback of SEBS is its complicated preparati¬ on method and the high price as a result of that. An example of materials which belong to the other main group of thermoplastic elasto¬ mers, thermoplastic/elastomer blends, are blends of polypropylene and ethylene/prσpylene rubber or ethylene/propylene diene rubber. In these blends the rigid polypropylene phase is the continuous phase and the soft phase is dispersed. Because the continuous phase is polypropylene the material has good oil resistance properties. These blends are made by blending the two main components and various additives in an extruder. Phase separation is obtained stabile by curing the dispersed rubber phase, look e.g. US 4,594,390. The invention in hand descibes a method to produce a thermoplastic elastomer with a polyolefine as a continuous phase and a rubberlike polyacrylate as a dispersed phase. This product is made in a reactor and the product can, if needed, be crosslinked already during the polymerisation in the reactor. Thus no separate vulcanisation stage is needed. Because the polyolefine is the continuous phase and because the elastomer in the product is a polyacrylate, the product has very good weather and oil resistance properties. Thus this invention makes it possible to produce a polyolefine based thermoplastic elastomer without a separate vulcanisation stage and with a polyacrylate as a dispersed phase. In this process the acrylate is polymerised into the polyolefine matrix. The acrylate is an acrylate which has elastic properties and which has a glass transition temperature below the room temperature. When acrylates are polymerised they form a dispersed phase in the polyolefine matrix. Because the acrylate is polymerised by the free radical polyme¬ risation technique, part of the acrylate chains are crosslinked to polyolefine chains, which causes the good adhesion between the continuous polyolefine phase and the dispersed polyacrylate phase. By using a smaller amount of diacrylate together with the acrylate the dispersed polyacrylate phase can be crosslinked to the desired amount. The inventively new in this patent is that the polyolefine / polyacrylate blend which is made by polymerising an acrylate into the polyolefine matrix has the polyolefine as a continuous phase and the polyacrylate as a dispersed phase from which the result is that the material has thermoplastic properties. Furthermore the material is characterised by the fact that the dispersed elastic polyacrylate phase can be crosslinked during the polyme¬ risation stage and the material can therefor be processed so that the structure of the dispersed polyacrylate part is not destroyed. The crosslinking of the polyacrylate phase is especially important in the cases when the adhesion between the polyolefine matrix and the polyacrylate can be expected to be low like in the case when polyolefine is homopoly- ethylene or polypropylene. By heating during the processing the polyolefine is melting and becomes fluid but the soft dispersed polyacrylate keeps its dispersed form because it is crosslinked. The actual production of the material can be made by some of the methods given in the patent literature in which monomers are polymerised by free radical polymerisation technique into polyolefine matrix, e.g. by the Finnish patent 88170. In principal the production is made so that acrylate monomer, and optionally diacrylate monomer, and the initiatior is absorbed into polyolefine particles. Impregnation temperature is so low that no decomposition of the initiator occurs, but however so high that the monomer and the initiator can penetrate into polyolefine particles. When all monomer and initiator has been absorbed, the temperature is elevated and the initiator decomposes and initiates the polymerisation of the acrylate. During the impregnation the polyolefine particles swall to some extend depending on the amount of monomer added, but the particles maintain their particle structure during the impregnation and also the polymerisation. The invention is next described in detail. Polyolefine Useful polyolefines include high density polyethylene, low density polyethylene and linear low density polyethylene. Polyethylene can be a homopolymer or a copolymer. The comonomer of ethylene can be vinyl acetate, vinyl chloride, propylene or some other *- olefin, CrC-V-alkylacrylate and -methacrylate, acrylic acid and methacrylic acid, hydroxy alkylacrylate and -methacrylate, glycidylacrylate and -methacrylate, dienes such as hexadiene-1,4, hexadiene-1,5, heptadiene-1,6, 2-methylpentadiene-l,4, octadiene-1,7, 6-methylheptadiene-l,5 and polyenes such as octatriene and dicyclopentadiene. Also ethylene-*-olefin-polyene-terpolymeres are useful. Useful *-olefϊns include propylene, butene, pentene, isoprene, hexene or their mixtures and useful polyenes include hexadie- ne-1,4, hexadiene-1,5, heptadiene-1,6, 2-methylpentadiene-l,4, octadiene-1,7, 6-methyl- heptadiene-1,5, octatriene, dicyclopentadiene. In case that the ethylene polymer is a copolymer, the share of ethylene must be at least 50 % by weight. The polyolefine can also be comprised of polypropylene and its copolymers. Propylene copolymers must consist over 50 % by weight propylene and can be random- or block co¬ polymer of propylene and ethylene. Also other *-olefines can be used as comonomers, and also dienes such as hexadiene-1,4, hexadiene-1,5, heptadiene-1,6, 2-methylpentadiene- 1,4, octadiene-1,7, 6-methylheptadiene-l,5 and polyenes such as octatriene and dicyclo¬ pentadiene. The polyolefine can be in any form, but most suitably in the form of pellets with a diameter 0,5 - 10 mm. When the polyolefine is in a particle form, the after treatment, washing and drying of the material is facilitated. Acrylate monomer Suitable monomers are acrylates and methacrylates the polymers of which have low glass temperatures, i.e. they are rubberlike at the room temperature and lower temperatures, preferably at the temperature below -20 | C.The glass temperature of the polyacrylate specifies the lower operating temperature of the material, below the glass temperature the polyacrylate is rigid and inelastic and the elastomeric properties of the material are lost. Suitable acrylates are alkylacrylates having 1 or preferably 2 or more carbon atoms in the alkyl chain. Methacrylates having a glass temperature low enough are alkylmethacrylates having 4 or more or preferably 8 or more carbon atoms in the alkyl chain. These monomers can be used alone or in mixtures of two or more monomers. Together with the above mentioned monomers, also smaller amounts of monomers having less carbon atoms in the carbon chain can be used.The glass temperature of the final product can thus be tailored. As comonomers one can further use acrylates and methacrylates which except that they have an ester bond also have other polar groups, e.g. alcoxy or hydroxy groups. Examples of these are methoxy- and ethoxyacrylate, hydroxyethyl- and hydroxypropylmet- hacrylate. By using these comonomers the oil resistance of the product can be improved. Also small amounts of other non-acrylate monomers that are polymerisable by free radical polymerisation technique can be copolymerised with the above mentioned acrylates and methacrylates. The amount of the acrylate In principal, as small amounts of acrylate as wanted can be added, but in order to achieve a material which can be said to be a thermoplastic elastomer, tens of per cents must be added. The amount of acrylate to be polymerised into the polyolefine depends also on the polyolefine which is used and on the possible addition of oil. A polypropylene based material needs, according to this invention, without oil and filler addition 50 - 90 % by weight acrylate, the share of polypropylene is thus 50-10 % by weight. For polyethylene based thermoplastic elastomers, according to this invention, the needed amount of acrylate is depentant on the polyethylene, if there is a comonomer or no. Without oil and filler addition the amount of acrylate can vary from 50 - 90 % by weight for homopolyethylene down to 20-90 % by weight for polyethylene qualities which contain up to 30 % by weight comonomers. The effect of the amount of the acrylate to the softness and other properties can be more clearly seen from the experiments. The addidion of oil By means of the oil addition the material can be softened. Alternatively it can be said that by the oil addition the amount of acrylate to obtain a certain softness can be reduced, compared to the amount of polyolefine. The amount of added oil can be 0-40 % by weight in the final product. Oil can be added together with acrylate and initiator and thus it can penetrate into the polyolefine particles during the impregnation and/or polymerisation. Oil can also be added to the reactor only after the finalised polymerisation and can be impregnated into polyolefine - polyacrylate particles at an elevated temperature. Further¬ more one way to add oil to polyolefine - polyacrylate particles is in an extruder. Usable oils are oils that are normally used to soften rubber, e.g. paraffinic, naphthenic, aromatic and synthetic oils as well as plasticisers for thermoplastics such as e.g. dioctylphthalat. The addition of fillers Furthermore one way to modify the material so that the properties of the product are desirable is to add fillers. By addition of fillers e.g. the rigidity and the operating temperature can be raised. The filler can be added to the polyolefine - polyacrylate blend in the extruder. The filler can of course also be included to the polyolefine which is used as raw material for the polymerisation. Conventional fillers can be used, e.g. talc, caolin, CaCO 3 , silica. The amount of fillers can be 0-70 % by weight in the end product. The composition of the end product The end product can thus besides polyolefine and polyacrylate also contain oil and fillers. The amount of polyolefine and polyacrylate in the end product can thus vary in very wide margins depending on the amount of oil and fillers and also on the chosen polyolefine. If the polyolefine is polypropylene, the ratio of polypropylene/polyacrylate can be 0.1-2. If the polyolefine is polyethylene, the ratio can vary from 0.1 to 5. Crosslinking of the polyacrylate Some acrylates form spontaneously gel without any diacrylate use. In such cases it is not always necessary to use diacrylate to crosslink the polyacrylate. One in the literature well- known example of an acrylate which spontaneously forms gel is butylacrylate. The need to use diacrylate depends also on the adhesion between the dispersed polyacrylate and the continuous polyolefine phase.If the adhesion between the phases is high, the tendency of the dispersed polyacrylate to agglomerate and build bigger phase structures is lower than in the cases where adhesion is poor. If the polyolefine is polyethylene which contains polar groups, the adhesion can be so good that only small amounts or no diacrylate at all is needed. If the polyolefine is a homopolyethylene or polypropylene the adhesion between the phases is low, the polyacrylate must be crosslinked with diacrylate in order to enable the processing of the dispersed polyacrylate without agglomeration and forming of big stuck polyacrylate blocks or without phase invasion which leads to the situation that the polyacrylate becomes the continuous or at least a cocontinuous phase. The crosslinking is is most conviniently made already in the reactor by adding an acrylate having two or more double bonds. During the polymerisation these acrylates having two or more double bonds are polymerising with different polyacrylate chains and the polyacrylate particles are crosslinking. Examples of the suitable crosslinking agents are hexanediol diacrylate or dimethylacrylate. The amount of the crosslinking agent is 0-15 % by weight based on the amount of acrylate. Because the amount of the crosslinking agent can be rather low, also other monomers, in addition to multifunctional acrylates, having two or more double bonds can be used without any remarkable influence on the properties of the product, e.g. divinylbenzene. Initiator Initiators which can be used to polymerising of acrylate are those initiators conventionally used in free radical polymerisation of vinyl monomers, being organic peroxides like e.g. benzoylperoxide, lauroylperoxide, t-butylperbenzoate, t-butyl-peroxy-2-ethylhexanate, t- butylperoxide, dicumylperoxide, di-t-butylperoxide, bis(t-butylperoxyisσpropyl)benzene, t-butylperoxyisopropylcarbonate, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, 2,5-dimethyl- 2,5-di-(t-butylperoxy)hexyne-3, and azo compounds like azobisisobutyronitrile and azobisdimethylvaleronitrile. More than one initiator can be used simultaneously so that the polymerisation starts at a low temperature with a "low temperature initiator" and continues with a "high temperature initiator" at a higher temperature. The amount of the initiator can be between 0.001 and 2 % by weight, preferably between 0.1 and 1 % by weight, based on 100 weight parts of monomer. Production, including impregnation and polymerisation In principal, the production of this polyolefine - polyacrylate material can be made by the methods presented in the patent literature in which the acrylate and the initiator are first initiated into polyolefine particles and the acrylate is thereafter polymerised by elevating the temperature. The impregnation of the acrylate and the initiator can thus be made in the total absence of water, by adding some water, by adding water when more than half of the acrylate has been impregnated (these three methods are in principal described in the Finnish patents FI85496, FI86642 and FI88170) or in the presence of the total amount of water (as in the US patent US 4.412.938). The impregnation can also be made so that into a water suspension, which contains polyolefine particles, is slowly added during several hours the acrylate and the initiator at an elevated temperature so that the impregnation and polymerisation are simultaneous (this method is described in the German patent DE 2.907.662). An advantageous method is the one according to the Finnish patent FI88170. By this method, maximum of about 65 % by weight of acrylate can be impregnated and polyme- rised into polyolefine in the polymerisation stage. If one wants to raise the amount of the polyacrylate more in order to get softer elastomer, it is possible to impregnate more acrylate into the product obtained from the first polymerisation stage and thereafter to polymerise. By this way the polyacrylate content can gradually be raised to near 100 % . This gradual raising of polyacrylate content does not necessarily be made in totally separate polymerisations. In the end of the first polymerisation, the temperature can be lowered to the impregnation temperature and the desired amount of acrylate and initiator can be pumped in. When the acrylate and the initiator have been absorbed into the particles, the temperature is raised and the acrylate polymerises. If the polymerisation is made in two or more stages and one wants to crosslink the polyacrylate, it is appropriate to make the first polymerisation without diacrylate. Thus the polyacrylate forms a dispersed phase during the first polymerisation stage because the polyacrylate chains are not crosslinked and therefor the polarity differences compared to the polyolefine phase are seeking each other. In the other polymerisation stage the added acrylate and diacrylate are mainly seeking their way to the polyacrylate particles already existing in the polyolefine matrice and crosslinking there. The added diacrylate will hardly react with the polyacrylate forming in the first polymerisation stage, but because the acrylate and diacrylate are polymerising in the presence of the already existing polyacryla¬ te, the latter will also be physically crosslinked, via so called engtanglements, to the chemically crosslinked polyacrylate formed in the second polymerisation stage. Properties of the polymerisation product Because the elastomer in this thermoplastic elastomer is polyacrylate, the product has especially good oil resistance, weather resistance and ageing resistance. The properties of the thermoplastic elastomers produced according this patent depend on the polyolefine used: homo, block or random polypropylene, homopolyethylene or polyethylene con¬ taining comonomers. The properties to which the choise of polyolefine has influence are especially the temperature resistance, chemical resistance and adhesion properties. The acrylate type, the amount of acrylate and the crosslinking density affect to the properties of the product, like hardness, toughness and elasticity. Characteristic to an ethylene based product is its good heat resistance and oil resistance. The properties of the product can of course be tailored by adding fillers. Fillers can also be part of the starting polyolefine. The properties of the product are described more in detail in the experiments. The usage of the product The material produced according to this invention can be used in the applications in which other thermoplastic elastomers or conventional rubber is used. Typical fields of usage are thus in the construction industry, e.g sealing lists and packages, in the motor industry e.g. protection bellows at power transmission points and interior material for instrument panels, in the electrical industry, e.g material for cables, contacts and different cases. This material can also be used to diverse mechanical articles like handles, wheels and sheaths. The material can be processed by conventional processing methods used for thermoplastics like e.g. extrusion, injection moulding and blow molding. Because polyolefine is the continuous phase, the material suits well to the coextrusion with polyolefines. In the processing, conventional additives like antioxidants, fillers and oil can be added. Examples 1-16 Polyolefine pellets, acrylate , initiator and possibly 1,6-hexanediole diacrylate were added to the reactor. The reactor was filled and emptied three times with 7-8 bar nitrogen in order to remove oxygen from the reactor. After that the temperature was raised to the impregnation temperature and kept there, stirring continuously, until the major part of the acrylate and the initiators were impregnated. The impregnation time was 1-3 hours depen¬ ding on the polyolefine quality. Thereafter, the suspension water, also rinsed with nitrogen, was added. The suspension water contained tricalsiumphosphate and sodiumdo- decylbenzenesulphonate as a suspension agent. The temperature of the suspension water was the same as the impregnation temperature. After the water addition the temperature was raised so much that the initiator started to decompose and initiate the polymerisation. The polymerisation took 7-12 hours depending on the polyolefine quality. The polyme- risation product was washed and dried after the polymerisation. Several different poly olefine - polyacrylate materials were made according to this model, see Table 1. All poly¬ propylene based materials having more than 50 % by weight acrylate were made in two stages so that the product from the first stage contained 50 % by weight acrylate.Experi- ment 9 was also made in two stages and experiment 10 was made in three stages. The structure with the dispersed polyacrylate domains can be seen from the Figure 1, where the product from the first polymerisation stage of the experiment 15 has been photo¬ graphed by a transmission electron microscope. In the picture, the dark dispersed phase is polyacrylate and the light continuous phase is polypropylene. From the figure it can be seen that the diameter of the polyacrylate particles is about 0.5 ≤m. Table 1. Experiments 1-16. Exp Polyolefine 1 MI Acrylate weight Diacry¬ Initiator Impre- Polym. Gel 2 Nr quality type 4 % late 6 type 5 \ c % w- 1 EVA28 5 EHA 40 - AIBN.BPO 37 55-100 62 2 EVA28 5 EHA 50 - AIBN.BPO 41 55-100 56 3 EVA18 10 EHA 50 - BPO.BPIC 51 75-115 61 4 EVA9 8 EHA 50 - BPIC 69 90-120 54 5 EBA27 4 EHA 50 - AIBN.BPO 44 55-100 77 6 EBA17 7 EHA 50 - BPO 72 70-100 70 7 EBA17 7 BA 50 - BPIC 61 85-115 55 8 EBA17 7 BA 50 1,0 BPIC 69 85-115 60 9 EBA7 1 BA 64 0,5 t-BPB 86 90-120 83 10 LLDPE 65 BA 69 1,6 DHBP 101 110-135 53 11 Random PP 20 BA 50 0,1 DYBP 116 125-150 53 12 Random PP 20 BA 68,5 1,6 DYBP 112 130-150 74 13 Random PP 20 BA 67 3,1 DYBP 108 130-150 67 14 Random PP 20 BA 74 1,5 DYBP 117 130-150 74 15 Random PP 20 EHA 68.4 1,6 DYBP 116 130-150 64 16 Block PP 40 BA 67 3,0 DYBP 120 135-150 76 1) All polyolefines used are Neste*s commercial qualities. 2) Gel content was measured in boiling xylene under 16 hours. 3) Melt index is determined for polyethylene qualities at 190 | Cand 2,16 kg and for polypropylene at 230 | Quid 2,16 kg. 4) EHA = ethylhexylacrylate, BA = butylacrylate 5) AIBN = a-obisisobutyronitrile, BPO = benzoylperoxide, BPIC = tert-butylpero- xyisopropylcarbonate, t-BPB = tert-butylperoxybenzoate, DYBP = 2,5-dimethyl 2,5- di(tert-butylperoxy)-hexyne-3, DHBP = 2,5-dimethyl 2,5-di(tert-butylperoxy) hexane. 6) Diacrylate = 1,6-hexanedioldiacrylate The polymer materials made according to Table 1 were injection moulded to sheets having the size of 80 x 80 mm and the thickness of 2 mm, at 165-205 | C, depending on the polyolefine used. The necessary test bars were punched from the sheets. The mechanical properties are in Table 2. Elongation at break and tensile strength have been measured from test rods which are punched transverse to the flow direction of the injection moulding. Table 2. Mechanical properties of the materials of the experiments 1-16. Exp. Polyolefine Acrylate % Di- Gel •long. tensile -RHD 3 compr. tension I Nr qualityt type acr. « at stre¬ set* * set 5 * w-S break 1 ngth 1 % Pa 1 EVΛ28 EHA 40 . 62 158 5,5 65 - 24 2 EVA28 EHA 50 . 56 177 3,2 52 - 17 3 EVA18 EHA 50 - 61 107 2,7 61 - 20 4 EVA9 EHA 50 - 54 90 3,2 75 - 23 5 EBΛ27 EHA 50 . 77 75 1,9 56 - 16 6 EHA17 EHA 50 . 70 449 5,4 67 - 16 7 EBA17 BA 50 . 55 528 6,1 75 30 33 8 EBA17 BA 50 1,0 60 354 7,1 76 20 25 9 EBA7 BA 64 0.5 83 209 6,3 75 22 16 10 L DPE BA 69 1.6 73 175 5,1 82 38 37 U Random PP BA 50 0,1 53 198 8,4 97 - 66 12 Random PP BA 68,5 1,6 74 169 7,3 90 43 40 13 Random PP BA 67 3,1 67 142 8,9 92 31 32 14 Random PP BA 74 1,5 74 128 5,6 81 26 16 15 Random PP EHA 68,4 1,6 64 127 5.9 88 43 43 16 Block PP EHA 72,5 3,5 1) Elongation at break measured by ISO 37 2) Tensile strength measured by ISO 37 3) Hardness, IRHD, measured by ISO 48 4) Compression set after 24 hours at room temperature by ISO 815 5) Tension set after 24 hours at room temperature by ISO 2285 The amount of polyacrylate has the biggest effect to the hardness of the product, the higher amount of polyacrylate the softer product, see experiments 1 and 2 and experi- ments 11-15. To the mechanical properties, the polyolefine quality also affects most to the hardness, compare 2, 3 and 4 as well as 5 and 6. The amount of diacrylate affects all mechanical properties. The higher amount of diacrylate improves strength, compression set and tension set but decreases the elongation at break, compare 7 and 8 as well as 12 and 13. In table 3 the product from the experiment 7 is compared with commercial SBS-quality, Dexcos Vektor-2411D, at 55 | C These both have about the same hardness and the same highest operating temperature, 60-70 | CFrom the table it can be seen that SBS has considerably lower oil resistance than the product from the experiment 7. Also, in table 3 is compared the product from the experiment 13 with the thermoplastic elastomer Santopren 201-80 at 100 | C.The product from the experiment 13 has polypropylene as a polyolefine and a continuous phase and it can therefor regarding to the temperature resistance, be compared with Santopren which also has polypropylene as a continuous phase. Santopren has ethylene-propylene-diene rubber as an elastomeric phase. The both have same hardness. From the table it can be seen that the product from the experiment 13 has considerably better oil resistance than Santopren in ASTM1- and ASTM2-oils. In ASTM3-oil Santopren is a little better. Table 3. Oil resistance, measured as swelling, of the material made according to this invention compared with commercial thermoplastic elastomers, by ISO 1817. For experiment 7 and SBS was used 55 | Quid for experiment 13 and Santopren was used 100 | c. Bx Nr Material Hardness ASTM1 ASTM2 ASTM3 BtHD lday 3days 7days lday 3days 7days ldsy 3day 7day* % % % % % % % % % 7 EBA17-PBA 75 8 14 16 14 28 34 51 89 - SBS,Ve__r-2411D 82 35 50 52 98 127 - - - - 13 PP-PBA 92 8 10 22 24 - 58 58 Ssmopren 201-80 91 18 19 31 31 - 52 54 The ageing resistance of the material at high temperature was tested by ageing the mate¬ rial at 70 I Ctiuring 168 hours. The elongation at break and tensile strength were measu¬ red for imaged and aged materials from test bars punched in flow direction. The material from experiment 7 was compared with a commercial SBS-quality, Enichem Europrene SOL T166, and with a commercial SEBS-quality, Neste Polymer Compounds 6503. These three materials are comparable by hardness and operating temperature. From table 5 it can be seen that the material from experiment 7 has considerably better ageing resistance at an elevated temperature. Apart from the fact that the material from experiment 7 was not stabilised with antioxidants. In the table there is also compared a polypropylene based material made according to example 13 with Santopren-quality 201-80. Table 5. Changing of the elongation at break and tensile strength during ageing at 70 | C for 168 hours. The chance is given as a per cent chance between the unaged and aged material. Exp Material Hardness 1RHD Elongation Tensile Chance, % Nr at break % strength MPa Elongation Tensile at break strength 7 EBA17-PBA 75 129 5.7 +4,9 +7,5 SBS 166 75 540 11.3 -15,2 -36,2 SEBS 6503 75 305 5,8 -21,0 -4,9 13 PP-BPA Santopren 201-80 91 126 10,3 -15.4 +5,1 Experiments 17-20 A material made according to experiment 7 but with a diacrylate amount 0,5 % by weight, was filled with three different fillers, 23-41 % by weight in the end product, in a screw extruder at 200 | CFrom table 4 can be seen that hardness is rising together with a rising filler content. Other mechanical properties remain unchanged when compared with the unfilled material of experiment 17. Table ..Influence of fillers on the mechanical properties of the product of experiment 17. Exp Polyole¬ Acryla¬ « Discr. Gel Elong. Tensile DtHD' compres¬ Tensi¬ Nr fine quali¬ te type weight % at str.' sion set* on set 9 ty * break 1 MPa « * % 17 EBA17 BA 50 0,5 63 360 6,6 78 28 32 18* EBA17 BA 50 0,5 - 270 6.2 84 24 32 19' EBA17 BA 50 0,5 - 238 6,0 87 30 39 20* EBA17 BA 50 0,5 - 322 7.1 87 27 41 1) Elongation at break measured by ISO 37 2) Tensile strength measured by ISO 37 3) Hardness, IRHD, measured by ISO 48 4) Compression set after 24 hours at room temperature by ISO 815 5) Tension set after 24 hours at room temperature by ISO 2285 6) Added filler talc, Finntalk 20 10 vol-% (23 % by weight) 7) Added filler CaCOj, Nordkrone 40 20 vol-% (41 % by weight) 8) Added CaCOj, Winnofil S 20 vol-% (40 % by weight) Experiments 21, 22 and 23 To a material which is made exactly according experiment 13 was added 10 % by weight oil and 0,3 % by weight antioxidant, Irganox 1520, in a single-screw extruder at 205 | C. A paraffin oil, Nypar 40 (Neste-Alfa Oy), and a naphthenic oil, Nytex 840 (Nyn |^-Petro- leum) were used as oils. The composition of the end product is thus 10 % by weight oil, 63 % by weight polybutylacrylate and 27 % by weight polypropylene. The material was injection moulded to sheets from which test bars were punched at flow direction. From the results in table 6 can be seen that by oil addition the material has become softer without the loss of other mechanically good properties, compression set and tension set have even improved. Table 6. Addition of 10 % by weight oil to a polypropylene-polyacrylate material. Exp. oil quality % by Elongation at Tensile IRHD» Compression Tension set 5 weight break 1 )- strength 1 sef % % MPa 21 138 9.3 93 37 32 22 Nyte 840 10 131 8,0 88 33 27 23 Nypar 40 10 142 8-5 89 33 25 1) -Elongation at break measured by ISO 37 2) Tensile strength measured by ISO 37 3) Hardness, IRHD, measured by ISO 48 4) Compression set after 24 hours at room temperature by ISO 815 5) Tension set after 24 hours at room temperature by ISO 2285 Experiments 24 and 25 These experiments were made in the same way as experiment 13 with the difference that to the reactor it was charged 6 % by weight oil together with the acrylate in the second polymerisation stage. The whole amount of oil was absorbed into the pellets and the end produces composition is thus 6 % by weight oil, 70 % by weight polybutylacrylate and 24 % by weight polypropylene. From the test results in table 7 down can be seen that the material, compared to experiment 13 becomes considerably softer and compression set becomes a little better. Elongation at break and tensile strength decrease a little. Experiment 26 This experiment was made in the same way as experiments 24 and 25 with the difference that oil was added in the both polymerisation stages, 6 % by weight in the first and 11 % by weight in the second polymerisation stage. This gives the final composition: 14 % by weight oil, 30 % by weight polypropylene and 56 % by weight butylacrylate (inclusive 2,2 % by weight diacrylate). Oil was Nytex 840. Test results can be seen in table 7 down. Experiments 27 and 28 As starting material for oil and filler experiments was used a polypropylene based material which was made according to experiment 13, with the difference that the amount of butylacrylate in the first polymerisation stage was 37 % by weight and in the second polymerisation stage 34 % by weight (+ 3 % by weight). This gives an end composition of 60 % by weight polybutylacrylate and 40, including 3 % by weight diacrylate. Table 7. Influence of oil and fillers to the properties. Exp. Oil quality w-% PP PBA Filler Elong. Tensile πuπy Compres¬ Tension 1 w-» w-% w-« at break str. 1 sion set 4 se, * MPa % 24 Nypa 40 6 24 70 - 118 6.9 84 31 31 25 Nytex 840 6 24 70 - 126 7,5 85 27 29 26 Nytex 840 14 30 46 - 27 Nypar40 20 28 Nypar40 20 1) Elongation at break measured by ISO 37 2) Tensile strength measured by ISO 37 3) Hardness, IRHD, measured by ISO 48 4) Compression set after 24 hours at room temperature by ISO 815 5) Tension set after 24 hours at room temperature by ISO 2285

Claims: Claims 1. A thermoplastic elastomer, characterised in that it consists of a polyolefine - poly¬ acrylate blend achieved by absorbing an acrylate monomer, initiator and eventually a diacrylate into polyolefine particles after which the temperature is raised and the acrylate polymerises into the polyolefine and forms a dispersed phase. 2. A thermoplastic elastomer, according to claim 1, characterised in that the polyacrylate has a glass temperature lower than room temperature, preferably under -20 | C. 3. A thermoplastic elastomer, according to claims 1-2, characterised in that monomers for the polyacrylate are alkylacrylates with 1 or preferably 2 or more carbon atoms in the alkyl chain, alkylmethacrylates with 4 or more or preferably with 8 or more carbon atoms in the alkyl chain, alkylacrylates and methacrylates which contain polar groups, like e.g. alkoxy- and hydroxy groups. 4. A thermoplastic elastomer, according to claims 1-3, characterised in that the polyacry¬ late can be crosslinked by copolymerising the acrylate with a diacrylate or a multifunc¬ tional acrylate during the polymerisation, when no separate vulcanisation stage is needed. 5. A thermoplastic elastomer, according to any of the preceding claims, characterised in that the polyolefine is polypropylene, polypropylene containing comonomers, polyethylene or polyethylene containing comonomers. 6. A thermoplastic elastomer, according to any of the preceding claims, characterised in that the weight proportion between the polyolefine and d e polyacrylate in the blend is 0.1-5. 7. A thermoplastic elastomer, according to any of the preceding claims, characterised in that 0-40 % of weight oil can be added into the polymerisation or during a separate extrusion stage in order to make the material softer. 8. A thermoplastic elastomer, according to any of the preceding claims, characterised in that the end product can contain 0-70 % by weight fillers. 9. A thermoplastic elastomer, according to any of the preceding claims, characterised in that it can simultaneously contain both oil and fillers. 10. A thermoplastic elastomer, according to any of the preceding claims, characterised in that it can be processed by conventional processing methods like extrusion, injection moulding, blow moulding and coextrusion with polyolefines. 11. A thermoplastic elastomer, according to any of the preceding claims, characterised in that it has good oil and weather resistance properties. 12. The use of a thermoplastic elastomer, according to claims 1-11, in construction and electrical industry, and also as mecanical articles like e.g. handles and in other applicatios in which other thermoplastic elastomers and conventional rubber is used.

Inventors: ILLMAN TARJA, LEHTINIEMI ISMO, VESTBERG TORVALD, ILLMAN, TARJA, LEHTINIEMI, ISMO, VESTBERG, TORVALD
Applicants: ILLMAN TARJA, LEHTINIEMI ISMO, NESTE OY, VESTBERG TORVALD, ILLMAN, TARJA, LEHTINIEMI, ISMO, VESTBERG, TORVALD
Application year: 1994
Main classification: C08F255
IPC codes: B62D1, C08F255, C08J3, C08L23, C08L33